Field of the Invention
The present invention relates to an image forming apparatus.
Description of Related Art
Heretofore, there are image forming apparatuses called tandem color image forming apparatuses having image bearing members corresponding to respective primary colors, i.e., yellow (Y), magenta (M), cyan (C) and black (K). This type of image forming apparatuses forms toner images on the image bearing members corresponding to the colors respectively and superimposes the toner images on an intermediate transfer member, and transfers the superimposed toner images of the four different colors to a transfer sheet to form a color image.
The respective image bearing members are driven by drive units which are provided for these image bearings respectively. The drive unit transmits rotation to a rotation shaft from a motor through a plurality of gears which reduces the rotation. The rotation shaft passes through the image bearing member which is cylindrical in order that the rotation shaft can be pulled out from the image bearing member, and is supported by a bearing on the opposite side to rotate the image bearing member.
The image bearing member receives rotation from the motor through a gear train consisting of a plurality of gears, and therefore each gear is required to have a necessary accuracy. Accordingly, a rotation irregularity, although which is small, can occur of the image bearing member under the influence of accumulated tolerance of the gears. Such a rotation irregularity of the image bearing member becomes a cause of image blurring.
From this fact, a drive shaft for transmitting a driving force from a motor or the like is connected to an image bearing member through a drive coupling which has play in order that a rotation irregularity does not increase when rotation is transmitted from the motor to the image bearing member through a gear train even if there is an error such as an eccentricity between the drive shaft and the image bearing member (for example, refer to Japanese Patent Published Application No. 2005-62806).
On the other hand, the rattling between a drive shaft and a drive coupling can be prevented by forming a spline on the outer peripheral surface of the drive shaft and grooves corresponding to the spline on the inner surface of the drive coupling (for example, refer to Japanese Patent Published Application No. 8-87225).
However, the prior art technique described in Japanese Patent Published Application No. 2005-62806 can prevent the rotation irregularity of an image bearing member from increasing, but cannot prevent the oscillation between the image bearing member and a drive shaft caused by the rattling therebetween. On the other hand, the prior art technique described in Japanese Patent Published Application No. 8-87225 can improve the rattling between a drive shaft and a drive coupling, but cannot prevent the deterioration of the rotation irregularity of the image bearing member associated with an oscillation caused by a small rattling occurring at the contact portion of a spline and the like during driving.
Accordingly, in accordance with the prior art techniques as explained above, there is a fear that a good image quality cannot be obtained due to the rattling of an image bearing member and the rotation irregularity of the image bearing member.
The present invention is made in order to solve such a prior art problem and it is an object of the present invention to provide an image forming apparatus capable of obtaining a good image quality without color shifts.